The present invention relates to a method for manufacturing a semiconductor device, and more particularly, to a wiring structure of a semiconductor device for burying an aperture such as a contact hole or a via hole and a method for manufacturing the same.
Generally speaking, the most crucial part in the manufacturing process of a semiconductor device is the wiring, because the operating speed, yield and reliability of the device are all determined by the wiring method. The step coverage of a metal layer is not a significant problem in a conventional semiconductor device having low integration. However, recently, higher integration levels have resulted in extremely small contact holes (i.e., diameters of one half micron or less) and very thin impurity injection regions in the semiconductor substrate. Using conventional aluminum wiring methods, it is difficult to fill a contact hole smaller than 1 .mu.m, and a void is often formed in the contact hole, and which lowers the reliability of the metal wiring layer.
In an early stage of manufacturing a semiconductor device, a metal wiring layer is formed on a silicon substrate by using pure aluminum. However, as temperature increases in a subsequent sintering stage, the formed aluminum layer absorbs silicon atoms from the substrate, which generates junction (Al) spiking. Therefore, Al-1% Si (aluminum supersaturated with silicon) has been widely used as the material of the metal wiring layer.
However, when the wiring of a semiconductor device is formed using Al-1% Si, silicon is extracted from the aluminum film during heat treatment at a temperature exceeding 450.degree. C., thus forming a silicon residue. In addition, a Si-nodule is formed in a contact hole through the solid-phase epitaxial growth of silicon atoms, to thereby increase the wiring resistance and contact resistance.
To prevent the above Al spiking, the generation of silicon residue and the Si-nodule due to an interaction between a metal wire layer and a silicon substrate, a diffusion barrier film is formed between the wiring layer and silicon substrate or between the wiring layer and an insulating layer. For example, a method for forming a titanium nitride (TiN) film as a diffusion barrier film on an inner wall of a contact hole is disclosed in U.S. Pat. No. 4,897,709 by Yokoyama et al. In addition, a technique where a double film consisting of a refractory metal (Ti) film and a TiN film is formed and heat-treated as a diffusion barrier layer, and a titanium (Ti) layer interacts with a semiconductor substrate to thus form a refractory metal silicide layer consisting of thermally stable compounds in the bottom of a contact hole connected to the semiconductor substrate, to thereby enhance a barrier effect, is disclosed in Japanese Laid-open Publication No. 61-183942. In general, such a diffusion barrier film is annealed in a nitrogen atmosphere. If the diffusion barrier film is not annealed, junction spiking occurs when aluminum or an aluminum alloy is sputtered at a temperature exceeding 450.degree. C. or when sintering is performed, which is not desirable. In addition, a TiN or TiW film is employed as the diffusion barrier film. A microstructural defect that cannot completely prevent the diffusion of aluminum or silicon at a grain boundary exists in the TiN or TiW film.
In addition, a method for blocking a diffusion path at a grain boundary by employing an oxygen stuffing method has been proposed (see: pp375-382 of "Effects of Oxygen on Reactively Sputtered TiN Films" by J. B. Stimmel and B. N. Mehrotra, in Tungsten and Other Refractory Metals for VLSI Application III, 1988). In general, when TiN is deposited and exposed to the ambient atmosphere, the exposed TiN is mixed with a small amount of oxygen in the atmosphere, to thereby increase a diffusion barrier effect. This is called a stuffing effect. In more detail, Stimmel and Mehrotra teach that oxygen exists in oxide form at a surface of barrier metal and at a grain boundary as well, which explains a stuffing effect.
However, a contact resistance may increase if a barrier layer formed by depositing Ti or TiN is exposed to the atmosphere, or if the TiN is deposited by mixing with oxygen, or if TiN is annealed at a nitrogen atmosphere mixed with oxygen. Accordingly, the barrier characteristic of a TiN film changes depending on the duration of atmospheric exposure, the amount of oxygen inflowed during deposition, the amount of oxygen in annealing, and the temperature. Annealing of the barrier layer is performed at a temperature of 450.degree. C. to 550.degree. C. under a N.sub.2 atmosphere for 30-60 minutes, which is known as an optimum condition.
However, the oxygen stuffing effect introduced when a diffusion barrier film is annealed causes oxidation of the surface of the diffusion barrier film, and thus causes problems such as contact characteristics when a contact hole is buried by using aluminum in the subsequent process. Thus, the oxygen stuffing effect degrades reliability of a semiconductor device. To suppress this degradation, a method for inserting a wetting layer for improving wettability of the metal layer and a method for burying a contact hole after forming a silylation layer and hydrogen-treating are proposed.
In another method, Si or O.sub.2 is ion-injected after a TiN layer, i.e., barrier layer, is heat-treated in order to enhance wettability between the barrier metal and aluminum wiring and to enhance a wiring quality and yield (Japanese Laid-open Publication No. 88-176035 by Higatta Masafumi).
In yet another disclosure, in the case where Ti is deposited in advance to an aluminum sputtering and a high temperature aluminum is subsequently deposited so as to fill a via hole whose size is 0.5 .mu.m and aspect ratio is 1.6, a filling-up effect decreases if Ti is thin (see: VMIC 170-176, 1991). However, as the size of a contact hole becomes smaller, i.e., below 0.5 .mu.m, the contact hole is not completely filled or a void is generated in the contact hole, to thereby degrade reliability.
FIGS. 1-3 are section views showing a conventional aperture (contact hole) buried wiring structure, wherein various problems which may arise in filling a contact hole are exemplified. First, an impurity diffusion region 4, which will become a source/drain region, is formed on a semiconductor substrate 2. Then, an insulating layer 8 having a contact hole 6 for partially exposing the surface of impurity diffusion region 4 is formed on the resultant structure. (Here, for the convenience of explanation, a gate electrode in MOS structure is not shown.) A titanium layer as an ohmic contact layer (not shown) and a TiN layer 10 as a diffusion barrier layer are sequentially formed on the inner sidewall surface of contact hole 6, on impurity diffusion region 4 exposed by contact hole 6 and on insulating layer 8. In addition, an aluminum layer 12 for filling contact hole 6 is formed on TiN layer 10.
Meanwhile, the above-described contact hole buried wiring structure can be manufactured as follows.
First, a field oxide film (not shown) is formed on semiconductor substrate 2 by a common local oxidation of silicon (LOCOS) method, and an impurity is deposited on semiconductor substrate 2 between the field oxide films, to thereby form impurity diffusion region 4 for forming a source/drain region. Then, an insulating material, for example, silicon oxide (SiO.sub.2), is deposited on the resultant structure by a common chemical vapor deposition (CVD) method, thereby forming insulating layer 8. Then, a photoresist pattern (not shown) for forming contact hole 6 is formed on insulating layer 8 which is then etched until impurity diffusion region 4 is exposed, using the photoresist pattern as an etching mask, to thereby form aperture 6. Then, titanium is deposited to a thickness of 300 .ANG. to 900 .ANG. by a sputtering method on the inner sidewall surface of aperture 6, on impurity diffusion region 4 exposed by aperture 6 and on insulating layer 8, to thereby form the ohmic contact layer. Sequentially, the diffusion barrier layer (layer 10) is formed on the Ti layer to a thickness of 600 .ANG. to 2000 .ANG. by a sputtering method. Aluminum is deposited on the resultant structure by a sputtering method, to thereby form aluminum layer 12 for burying aperture 6.
In the above-described conventional contact hole buried wiring structure and a method for manufacturing the same, a Ti layer (i.e., ohmic contact layer), a TiN layer 10 (i.e., diffusion barrier layer), and an Al layer 12 are formed by mainly a sputtering method. However, deposition by a conventional sputtering method causes a void 14 as shown in FIGS. 1 and 2, as the aspect ratio of the contact hole increases, to thereby degrade the reliability of a manufactured device. Also, according to the conventional technique, the step coverage of an aluminum layer is poor, as shown in FIG. 3, so that wiring shorts tend to occur. Thus, a reliability of the device is degraded.
FIG. 4 illustrates an initial nucleation of an aluminum film when aluminum is deposited on the diffusion barrier film shown in FIGS. 1-3, and includes an enlarged view of the sidewall portion showing the initial nucleation. Here, a reference numeral 10 denotes a TiN layer, 10a denotes a TiN grain, 12 denotes an aluminum layer, and 12a denotes an aluminum grain. A characteristic of the TiN layer formed in the inner sidewalls of an aperture and a surface morphology of an aluminum layer will be explained with reference to FIG. 4.
Since the surface of the TiN layer formed on the inner sidewall surface of an aperture is structurally perpendicular to the target when deposition is performed, a relatively small amount of sputtered atoms are deposited. Such tendency occurs obviously when a collimation technique is employed. In addition, since TiN is apt to grow in the &lt;111&gt; direction, columnar grains 10a are formed.
Meanwhile, in general, a TiN layer obtained by a sputtering method or CVD method is not amorphous. Therefore, the inner sidewalls of the contact hole where relatively few sputtered atoms are formed has a rough surface. Accordingly, an initial deposition characteristic of an aluminum atom formed on the rough diffusion barrier film is poor. In other words, a nucleation of aluminum around the relatively large TiN grains does not occur uniformly, and the aluminum is deposited unevenly and discontinuously as shown in the enlarged view. Therefore, even though heat treatment is performed by depositing aluminum in a contact hole during a subsequent process, a void is generated, and generation of such a void becomes easier in a contact hole having a high aspect ratio. Thus, reliability of a semiconductor device is degraded.